This invention relates to a lubricating composition suitable for metal forming (or working) such as plastic working, e.g., cold forging, of metals, particularly of aluminum and alloys thereof and a process for forming the metal using such a lubricating composition.
Aluminum and alloys thereof are light-weight and have good appearance and quality, so that they are widely used as sash door and window frames, cans, domestic appliance parts, and the like. These parts are almost made by plastic working with high productivity. Processes for plastic working change depending on structure, reduction of area, etc., of parts, but considering economic merit, cold forging is going to be employed mainly. Generally speaking, in the case of parts made of aluminum or an alloy thereof, since demands for surface state (gloss) due to serious consideration of appearance and dimensional accuracy are high, a special lubricant is used for the working, unlike a lubricant for plastic working of steel stock. Heretofore, in the cold forging of aluminum or an alloy thereof, there have been used lubricants comprising a mineral oil as a base oil, an oilness agent such as a fatty acid, a fatty acid ester, a higher alcohol, or the like, and an extreme-pressure additive such as tricresyl phosphite, trilauryl phosphite, or the like or a solid lubricant such as graphite, molybdenum disulfide, or the like. These compositions of lubricants are considered mainly so as to give good surface state after the working. Thus, these lubricants are only suitable for working with a small deformation amount and low in reduction of area. In the case of making formed articles with high reduction of area causing high temperatures and high surface pressures or with complicated shapes, since these lubricants are insufficient in resistance to load and heat resistance, they are limited in their applications due to the generation of cracks, surface roughening, deformed parts caused by non-uniform plastic flow, galling (or seizure), and the like.
In order to improve galling (or seizure) resistance which is one of important properties of lubricants for working (or forming), there is employed a process wherein the amount of oil to be taken into friction surfaces of a mold and a workpiece is increased at the time of working. That is, the improvement of wettable properties and affinity of the lubricant to a workpiece is aimed at. For example, there is proposed a lubricant for aluminum working comprising one or more mono- or di-phosphate esters of a polyoxyalkylene alkyl ether or polyoxyalkylene alkylphenyl ether, one or more C.sub.12 -18 saturated or unsaturated fatty acid esters or higher alcohols, one or more metal soaps, and a mineral oil (Japanese Patent Unexamined Publication No. 38797/83}, or a lubricant comprising a mineral oil, a polyoxyalkylene derivative, either alone or a mixture of a partial ester of higher carboxylic acid with a polyhydric alcohol and a higher alcohol, and a phosphur compound (Japanese Patent Unexamined Publication No. 26997/81). But, even these lubricants have problems of easily bringing about worsening of surface state, galling, cracks and the like in the case of high reduction of area being required or of forming shaped article parts having complicated shapes.
On the other hand, there is proposed a process for working a metal piece comprising pre-treating the surface of a workpiece with a chemical film, followed by subjecting to working after coating a metal soap on the surface. According to this process, good performance is exhibited without causing galling even in the case of high reduction of area being required, but surface appearance is poor due to, for example, coloring of the surface with the treating agent, which results in making it necessary to conduct finish working by mechanical working, or the like. Therefore, this process cannot be said as a general purpose lubricating process. Further, this process has disadvantages in that complicated steps are necessary for lubricating treatment, and control of the treating solutions is necessary.